Timing measurements are used in various types of wireless communication networks, for a variety of purposes. For example, Timing Advance (TA) measurements are used in certain types of wireless communication networks, such as those based on the Global System for Mobile Communications (GSM) and Long Term Evolution (LTE) standards. While substantive details are available in the relevant Technical Specifications, e.g., TS 36.133 and TS 36.321 for the LTE case, it may be helpful to explain the basics of TA. A User Equipment (UE) initiates a Radio Resource Control (RRC) connection with a supporting LTE network by sending a Random Access Preamble to an eNB, i.e., an LTE base station, also referred to as an eNodeB. The eNB uses the transmission from the UE to estimate the one-way propagation time for the transmission from the UE and sends a corresponding TA value to the UE, for use by the UE in time aligning its transmissions. In particular, the UE adjusts its uplink transmission timing a defined number of subframes after receipt of the TA value in a given sub-frame.
Of course, TA determination is only one of many examples. Both mobile wireless communication devices (e.g., UEs) and base stations, e.g., eNBs, make various timing measurements, including timing-based range measurements at various times and for various reasons, including for positioning. The various examples of timing-based range measurements include receive-transmit time difference measurements. At a UE, for example, the Receive-Transmit (Rx-Tx) time difference measurement is defined as the time difference between the receive timing of downlink radio frame #i at the UE, and the UE transmit timing of uplink radio frame #i. At the eNB, the Rx-Tx time difference is defined as the difference between the receive timing of uplink radio frame #i (for the path that is first detected in time) and the transmit timing of the downlink radio frame #i. See TS 36.214 for more detailed timing measurement examples in the LTE context.
The current version of TS 36.133 also specifies requirements on UE capabilities for support of event triggering and reporting criteria. The current requirements are primarily defined for the mobility measurements. The requirements include: a set of reporting criteria categories; the number of reporting criteria per category that UE shall be able to support in parallel; and the maximum total number of reporting criteria. The current set of reporting criteria in Rel. 9 includes three measurement categories used for mobility: intra-frequency, inter-frequency and inter-RAT measurements, as well as for legacy positioning measurements, namely OTDOA RSTD and UE Rx-Tx time difference measurements.
For the intra-frequency category, measurements for up to nine E-UTRAN intra-frequency cells may be configured in parallel. For the inter-frequency category, measurements of up to seven E-UTRAN inter-frequency cells and four positioning measurements may be configured in parallel. And for inter-RAT, up to five parallel measurements per supported RAT are supported. The maximum total number of reporting criteria is currently twenty-five. This means that, depending upon the UE capability (e.g. inter-RAT capabilities), an eNode B can configure a UE to perform up to twenty-five measurements in parallel. As long as the measurement configuration does not exceed the reporting criteria requirements above, the UE is required to meet the relevant performance requirements, e.g., measurement reporting delay, measurement accuracy of the configured measurements, etc.
Although these and other example timing measurements are well known in the wireless communication arts, the continuing evolution of wireless communication networks presents numerous issues, which are not well understood in the context of, for example, multipoint transmission/reception scenarios, including Distributed Antenna Systems (DAS), service involving multiple Remote Radio Heads (RRH), Multiple-Input-Multiple-Output (MIMO) service, in at least some cases, Coordinated Multipoint (CoMP) service scenarios, and diversity transmission scenarios. Complications not addressed in conventional approaches to timing measurements also arise in Carrier Aggregation (CA) service scenarios.
CA, also referred to as multi-carrier service, allows a UE to receive and/or transmit data simultaneously over more than one carrier frequency. Each carrier frequency is often referred to as a component carrier (CC) or simply a serving cell in the serving sector. Notably, CA is supported for both contiguous and non-contiguous component carriers, and component carriers originating from the same eNB need not provide the same coverage.
CA is used in both LTE and High Speed Packet Access (HSPA), and when CA is in use, a UE will have a primary serving cell (Pcell) and one or more secondary serving cells (Scells) operating on a secondary carrier frequency or frequencies. For the downlink, the carrier corresponding to the Pcell is the Downlink Primary Component Carrier (DL PCC), while in the uplink it is the Uplink Primary Component Carrier (UL PCC). Depending on UE capabilities, the Scells and the Pcell form a set of serving cells for the UE.
The above scenarios all may be regarded as involving “multifarious” radio links. One radio link is multifarious with respect to another radio link if the two links are opposite in terms of uplink and downlink transmit directions and further if they connect different pairs of radio nodes, i.e., the two links are not between the same pairing of two radio nodes in a network, and/or if they are associated with different cell identifiers. Different cell identifiers for two radio links implies two base stations that are geographically separated and/or implies the use of different carrier frequency bands for the two radio links. The use of multifarious radio links introduces significant challenges with respect to timing measurements, including the various timing-based range measurements associated with, e.g., mobile device positioning.